An ad hoc network in a radio system is normally a network consisting of only radio terminals without intervention of a base station and, for communication with a radio terminal existing in a zone outside a reach of radio waves, i.e., in an uncommunicable zone, packets are transported via radio terminals existing between the source and destination terminals, up to the destination, thereby securing communication.
Therefore, the radio terminals in the ad hoc network have the relaying function and share their own resources for communication of other terminals. This ad hoc network is essentially a self-supporting system like LAN and system for easily constructing a network to secure a communication area.
In recent years, however, studies are under way on applying the technology of such an ad hoc network to the public systems.
The application of the ad hoc network to the public services is mainly to supplement service areas. It is not economical in terms of capital investment to cover all the areas up to sites to which radio waves are hard to reach, e.g., behind buildings. The application of the ad hoc network technology can implement transfer from the system in which the network is entirely in charge of the area covering function, to the system in which some radio terminals supplementally contribute to the function.
Techniques of controlling transport routes on the ad hoc network have actively been studied as the most important technology for implementing this system.
In the ad hoc network, where a radio terminal moves, or where the communication quality heavily degrades, a variety of controls become necessary: for example, it becomes necessary to change a transport route from the source radio terminal to the destination radio terminal to another, to notify relay radio terminals of a forwarding address, and so on. Techniques for these controls can be settled by use of the technologies in wireless LAN, though there is the difference in that communication is conducted via the base station in the public system, and a number of proposals have been made in practice (e.g., Japanese Patent Application Laid-Open No. 11-289349 and others).